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2.Motion in Straight Line
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A Tennis ball is released from a height $h$ and after freely falling on a wooden floor it rebounds and reaches height $\frac{ h }{2} .$ The velocity versus height of the ball during its motion may be represented graphically by
(graph are drawn schematically and on not to scale)
A
B
C
D
(JEE MAIN-2020)
Solution
Velocity at ground (means zero height) is non- zero therefore one is incorrect and velocity versus height is non-linear therefore two is also incorrect.
$v^{2}=2 g h$
$v \frac{d v}{d h}=2 g=c o n s t$
$\frac{d v}{d h}=\frac{c o n s t a n t}{v}$
Here we can see slope is very high when velocity is low therefore at Maximum height the slope should be very large which is in option $3$ and as velocity increases slope must decrease there for option $3$ is correct.
Standard 11
Physics
